This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to Appln. No. 101 27 289.8 filed in Germany on Jun. 5. 2001; the entire content of which is hereby incorporated by reference.
The invention relates to a fuel supply system that supplies a fluid, that is to say gaseous or liquid, fuel to a burner arrangement with at least one burner, in particular a gas turbine. The invention also relates to a method for operating such a fuel supply system.
Particularly in the case of power plant technology, specifically with gas turbines, fuel supply systems of this type are used in order to supply sufficient fuel to a burner arrangement that is operated in order, for example, to heat a combustion chamber of a gas turbine. Such a burner arrangement can have one or more burners. Particularly in the case of an annular combustion chamber, a plurality of burners can be combined to form an annular burner arrangement. The fuel supply system is connected to a fuel feed line that feeds the fuel to the fuel supply system. A control valve is arranged in this fuel feed line. The feeding of fuel into the fuel supply system can be controlled by actuating this control valve.
A gas turbine is usually operated in a relatively steady-state fashion such that important parameters such as, for example, combustion chamber pressure and fuel mass flow are constant. A variation in the operational performance of the gas turbine can take place essentially through influence exerted on the fuel mass flow that passes via the burner arrangement into the combustion chamber. In other words, the burner output forms an important parameter for exerting influence on the turbine operation. Consequently, the fuel mass flow fed to the burner arrangement via the fuel supply system can be controlled in order to set or adjust turbine operating states. Provided for this purpose is a power control unit that determines as a function of a required burner output a fuel mass flow that must be fed to the burner arrangement by the fuel supply system. A valve control unit actuates the control valve as a function of the fuel mass flow thus determined in order thereby to feed the determined fuel mass flow into the fuel supply system.
However, it has emerged, particularly in the case of rapid transients, for example combustion chamber pressure and/or fuel mass flow, that a marked deviation can occur between the fuel mass flow fed into the fuel supply system by the actuation of the control valve and the fuel mass flow fed thereupon to the burner arrangement by the fuel supply system. This difference is ascribed to the volume, which can be substantial in some circumstances, of the fuel supply system, and to the compressibility of the fuel enclosed therein. Furthermore, this difference is influenced by a flow resistance of the system that occurs, in particular, at the transition between the supply system and the combustion chamber, that is to say at the burner nozzles. This deviation gives rise to an undesired operational performance in the case of a nonstationary operation of the burner arrangement and/or the gas turbine.
The invention aims to provide a remedy here. The invention as defined in the claims addresses the problem of specifying for a fuel supply system a possibility of being able to set more effectively the fuel mass flow fed to the burner arrangement.
This problem is solved with the aid of a method having the features of claim 1. The invention is based on the general idea of firstly determining from the required burner output a first setpoint for the fuel mass flow with which the burner arrangement must be supplied, in order to be able to furnish the required burner output. With the aid of this first setpoint of the fuel mass flow and, in particular, taking account of the current operating state of the fuel supply system, a second setpoint is then determined for the fuel mass flow, which is selected such that the burner arrangement is supplied with the previously determined first setpoint of the fuel mass flow by the fuel supply system fed with said second setpoint. This means that there is determined from the required first setpoint a second setpoint that, upon being fed into the fuel supply system in the current operating state has the effect that the fuel supply system outputs the desired first setpoint to the burner arrangement. The dynamic effects of the fuel supply system, for example owing to the compressibility of the enclosed volume of fuel, can be more or less eliminated by means of the mode of procedure according to the invention. The burner performance can therefore be set directly to the desired value without a time delay and without undefined intermediate states. The advantages in connection with the operation of a gas turbine fitted with a fuel supply system, in particular in a power plant, are patently obvious.
The fuel temperature in the fuel supply system can be taken into account when determining the second setpoint of the fuel mass flow. Alternatively, or in addition, it is also possible to take account of the combustion chamber pressure prevailing in a combustion chamber connected downstream of the burner arrangement. Moreover, it is also possible to take account of the volume of the fuel supply system that is filled with the fuel, as well as of the overall exit cross section of all the burners of the burner arrangement from which the fuel exits into the combustion chamber. The current operating state of the fuel supply system can be more or less characterized with the aid of these parameters, it thereby being possible to take account more or less of the current operating state of the fuel supply system when determining the second setpoint for the fuel mass flow.
The problem on which the invention is based is also solved by a fuel supply system having the features of claim 8. Here, as well, the invention is based on the general idea of firstly determining a first setpoint for the fuel mass flow as a function of the required burner output, and then determining a second setpoint for the fuel mass flow as a function of this first setpoint, in order, finally, to actuate the control valve as a function of the determined second setpoint. The determination, in particular calculation, of the second setpoint of the fuel mass flow is performed in this case by means of a dynamic correction unit that determines the second setpoint dynamically as a function of the previously determined first setpoint such that the burner arrangement is supplied more or less exactly with the desired first setpoint by the fuel supply system fed with said second setpoint.
In one particular embodiment, the dynamic correction unit is interposed between a power control unit determining the first setpoint and a valve control unit actuating the control valve, the output signals of the power supply unit, that is to say at least the first setpoint of the fuel mass flow, being fed to the input of the dynamic correction unit, and the output signals of the dynamic correction unit, that is to say at least the second setpoint of the fuel mass flow, being fed to the input of the valve control unit. The valve control unit then actuates the control valve as a function of this second setpoint, such that the second setpoint of the fuel mass flow is consequently fed to the fuel supply system. This specific embodiment has the advantage that it can subsequently be integrated in a particularly simple fashion into an already existing system in which the dynamic correction unit is incorporated in the data and/or signal stream in the manner of a series connection between the power control unit and the valve control unit.
Further important features and advantages of the invention follow from the subclaims, from the drawing and from the associated description of the figure with the aid of the drawing.